Cows are my friends. But their collective gifts to bucolic scenery, ice cream and the sale of barbecue sauce may be overshadowed by their contributions to global warming. The post-digestive gas deposits—burps and flatulence—of easy-going bovines compose almost one-fifth of the world's greenhouse gas emissions.

Cattle who have never driven an SUV, invested in coal or wasted a single kilowatt-hour in their lives are the target of initiatives, including a recently failed carbon tax of $175 per head. Despite the subsidies paid to cattle ranchers, this tax would have resulted in a spike in prices for dairy and beef. But such a spike might have repositioned cows in the public consciousness, given us a peek behind those Clover billboards and beyond the Gary Larson cartoons where ruminators stand on two legs and have funny conversations when no one is watching.

Common cattle management is actually neither cute nor clever, given the environmental problems it causes, although some herds are raised sustainably in small operations. The problem is scale. There are too many cows for the earth to sustain, and the number is expected to increase. Authors of the oft-cited global study "Livestock's Long Shadow," calculate that the 229 million tons of meat being produced at the start of this decade will rise to 465 million tons by 2050. That's more than double. Also in this report is the summary of environmental impacts caused by crowding the planet with cattle.

The report found that on a global scale, cattle:

• produce 37 percent of the anthropogenic methane, possessing 23 times the global warming potential of CO2;

• occupy 70 percent of the deforested Amazon;

• threaten more than half of the world's biodiversity hotspots and almost half of the world's ecoregions;

• produce 65 percent of anthropogenic ammonia emissions, contributing to acid rain and acidification of ecosystems;

• and use 8 percent of the world's water, mostly to water feed crops.

This is just a partial list. In the United States alone, the report says, cattle are responsible for "55 percent of erosion and sediment, 37 percent of pesticide use, 50 percent of antibiotic use and a third of the load of nitrogen and phosphorus into freshwater resources."

What to do? The worst idea I found was cooked up at the University of Alberta in Canada, where the Frankenfood crowd wants to reengineer a cow that burps less. A saner approach by a national food distributor, Stonyfield Farms, is a burp-reduction diet plan for dairy cows in the land of Ben and Jerry's—that would be Vermont.

Over a bowl of Cherry Garcia, I pondered the idea that if my ice cream came from a cow on a methane-reduction diet—say alfalfa, flax or hemp—I might be on a lower fat diet, too. According to Stonyfield Farms, the cow diet not only reduced emission up to 18 percent, but as a happy accident also reduced saturated fats in the milk. (Don't rush out for ice cream yet, as the Vermont cows in the study are busy making organic yogurt at the moment.) The big claim by this distributor is, "If every U.S. dairy were to adopt this approach, in less than one year the amount of greenhouse gas emissions we could reduce would be the equivalent of taking more than half a million cars off the road!"

Take half a million cows off the planet, daily, for several years, and far more problems might be solved. Because it isn't just about the burps and farts of cattle; it's the degradation of land and water caused by too many cows and their drain on resources needed to sustain life on this planet. When the EPA proposed the per-cow carbon tax last year, cattle-industry lobbyists conveniently transformed livestock into sacred cows. This was followed by sacred cheese, created by government subsidies attached to 102,000 tons of American dairy products for export. What can we do to change the practices and the herd sizes of an industry managed unsustainably and propped up by subsidies? The most powerful thing we can do right now is change how we eat.

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